Quantitative Estimation of the Carbohydrates. 107 



ance between the values obtained by this method of estimation and 

 that of the reducing power. 



The problem of determining the different sugars in the leaf is 

 one of extraordinary difficulty owing to the large number of members 

 of the group and the similarity of their properties. At present we 

 cannot regard as settled even the question of what sugars are 

 definitely absent from the leaf. This question is nevertheless of 

 much importance in the quantitative estimation of sugars in the 

 leaf and as the results of such analyses are likely to be used in 

 connection with theories of assimilation, the exact identity of the 

 leaf sugars may be of fundamental importance in obtaining an 

 understanding of the assimilatory process. 



It seems to us, therefore, that before forming a final judgment 

 as regards the carbohydrates of the leaf and before accepting in all 

 their details the results of quantitative analyses already made, there 

 is required a thorough investigation that will settle which carbo- 

 hydrates are present and which are not, as definitely as WiUstatter 

 has settled the question of the leaf pigments. 



In the following sections of this chapter we summarise the 

 analytical methods employed for quantitative carbohydrate analysis 

 of the leaf and the results obtained by their means, but it should 

 be understood that some of these results may have to be modified 

 when fuller knowledge is obtained of this important but extremely 

 difficult subject. 



D. Quantitative Estimation of the Carbohydrates 

 OF the Leaf. 



The quantitative estimation of the carbohydrates of the leaf 

 was first seriously undertaken by Brown and Morris for Tropceolutn ; 

 their results are given in their well-known paper in the Journal of 

 the Chemical Society for 1893. Since then the most noteworthy 

 contributions to the subject are those of Parkin (1911) on the 

 snowdrop {Galanthus nivalis L.) which embodies the results of a 

 careful series of observations extending over several years, and the 

 recent work at Rothamsted of Davis, Daish and Sawyer who have 

 called attention to several sources of error in the methods of earlier 

 workers. With the results obtained by tiiese different investigators 

 we shall deal in the next section of this chapter. We shall here 

 devote a little space to the description of the methods evolved by 

 these various workers for this extremely difficult analysis. 



